Exercise, oxidants, and antioxidants change the shape of the bell-shaped hormesis curve

Abstract

It is debated whether exercise-induced ROS production is obligatory to cause adaptive response. It is also claimed that antioxidant treatment could eliminate the adaptive response, which appears to be systemic and reportedly reduces the incidence of a wide range of diseases. Here we suggest that if the antioxidant treatment occurs before the physiological function-ROS dose-response curve reaches peak level, the antioxidants can attenuate function. On the other hand, if the antioxidant treatment takes place after the summit of the bell-shaped dose response curve, antioxidant treatment would have beneficial effects on function. We suggest that the effects of antioxidant treatment are dependent on the intensity of exercise, since the adaptive response, which is multi pathway dependent, is strongly influenced by exercise intensity. It is further suggested that levels of ROS concentration are associated with peak physiological function and can be extended by physical fitness level and this could be the basis for exercise pre-conditioning. Physical inactivity, aging or pathological disorders increase the sensitivity to oxidative stress by altering the bell-shaped dose response curve.

Graphical abstract

Fig. 1

The hypothetical adaptive range. The middle of the graph represents the optimal zone of the dynamic homeostasis, while the outer line indicates the biological limitations, which cannot be reached without risk of death. The line, called functional limitation, shows the capacity of each individual and it is a mobile value. The functional/actual limit can be readily altered by exercise training. Aging decreases the rate of adaptive response, and the capacity to maintain homeostasis is decreasing, as demonstrated by the white arrows.

Fig. 2

Supplementation of antioxidants before (-) the ROS levels reach the value associated with peak physiological function that can attenuate the beneficial effects of exercise. On the other hand antioxidant treatment, after (+) the period of maximum ROS-associated function can result in decreased appearance of fatigue and/or improved function.

Fig. 3

Exercise with different intensities, using different pathways (anaerobic alactic (AA), anaerobic lactic (AL) and aerobic (AE), to reproduce ATP. Due to the intensity of exercise the causative reason for fatigue and recovery would be dependent on the intensity of exercise. The production of ROS is also dependent on intensity: greater intensity is paired with greater production of ROS. The recovery period to the normalization of ROS production is not well known.

Fig. 4

The “A” curve is a typical dose-response curve to physical exercise. Moderate exercise increases the physiological function of different organs, increases the rate of prevention against diseases and improves quality of life. Physical inactivity, strenuous exercise and overtraining increase the risk of diseases and decrease physiological function. The “B” curve indicates that regular exercise can extend or stretch the levels of ROS that are associated with high levels of physical function. This means that exercise can increase tolerance against high levels of ROS and can be preventive against oxidative stress- associated diseases.